Conventionally, in a semiconductor device manufacturing field, a desired pattern is formed on a substrate such as a semiconductor wafer or the like by performing film formation or etching. In such a semiconductor device manufacturing process, if an STI (Shallow Trench Isolation) process is carried out, deposits of silicon oxide (e.g., SiO2 or SiOBr) are deposited on a sidewall of the pattern. In a conventional case, such deposits are removed by a process using, e.g., a single gas of HF (hydrogen fluoride).
However, when a composition or a bonding state of deposits is similar to that of silicon dioxide (e.g., a gate oxide film) as a structure in a pattern, the selectivity therebetween is not obtained. Moreover, water as a by-product generated by the reaction between the deposits and HF (SiO2+4HF→SiF4+2H2O) accelerates the reaction. Thus, the chain reaction occurs, and the silicon dioxide as a structure in the pattern may be etched as well as the deposits.
If the exposure time (q-time) after the etching process is increased, the selectivity may deteriorate further due to the effects of moisture depending on the moisture absorbing state of the deposits. As for a technique for removing a natural oxide film formed on a surface of a silicon substrate, there is known a technique using HF vapor, H2O vapor or alcohol vapor (see, e.g., Japanese Patent Application Publication No. H07-263416). However, this technique is used for removing a natural oxide film, but not for removing deposits deposited on a sidewall portion of a pattern.
As described above, in a conventional case, when deposits deposited on a pattern are removed, the selectivity between the deposits and the silicon dioxide as the structure in the pattern is low, and the silicon dioxide as the structure in the pattern is damaged. If the exposure time (q-time) after the etching process is increased, the selectivity deteriorates further due to the effects of moisture depending on the moisture absorbing state of the deposits.